Well, you are not yet Petrosian so you can't give away queens. I noticed from the chart that your form has big ups and downs. You win against 1900, then you lose to 1400. What the hell is that all about? The weaker the player, the more ups and downs he has. 1800 rated players have steady performance but you... I don't know. What's your rating now?

Petrosian dropped his queen only a few times. A typical master will miss a simple tactic in approximately 1/150 games. On the contrary, you miss simple tactics every tournament. That is why something is wrong.

Alot of famous chess players have blundered away queens, and even mate in ones... http://www.chessbase.com/newsdetail.asp?newsid=3514

In order to avoid blunders I think you should do a lot of tactics, and not just from emrald, because that mainly helps your quickness in spotting tactics and pattern recognition.

Here are some really good ones out there:

Sharpen your tacticsMaster Challange

I hope that helps. And also, I have seen some people post stuff such as your opening with d4 is bad, you block in your c1 bishop; but really opening does not matter in this level as long as you get an equal position.